Workpiece holder, semiconductor fabricating apparatus, semiconductor inspecting apparatus, circuit pattern inspecting apparatus, charged particle beam application apparatus, calibrating substrate, workpiece holding method, circuit pattern inspecting method, and charged particle beam application method

ABSTRACT

The present invention is intended to highly fast, stably acquire highly accurate images from irradiated positions with an electron beam on a circuit pattern in the step of fabricating a semiconductor device including an insulating material or a mixture of an insulating material and a conductive material, without occurrence of any deviation in the irradiated position in the images to be comparatively inspected, automatically comparing the images with each other thereby inspecting defects of the circuit pattern without occurrence of errors, and feeding back the result to the conditions of fabricating the semiconductor device thereby increasing the reliability of the semiconductor device and reducing the defective percentage thereof. The dependence of the surface height of a workpiece on the corrected amount of deflection at a central portion of a workpiece stage is compared with that at the outer peripheral portion of the workpiece, to obtain a distortion amount inherent to the outer peripheral portion of the workpiece. The distortion amount is eliminated from an outer peripheral standard mark signal, to calculate the dependence of the height on the corrected amount of deflection at the outer peripheral portion, thereby obtaining the deflection correcting amount at the outer peripheral portion equivalent to that obtained at the central portion. Since a suitable deflection correcting table can be prepared only by using the outer peripheral standard mark, the deflection correcting table can be updated by repeating desired times calculation of the corrected amount of deflection at the outer peripheral portion while a wafer is left mounted. As a result, the deflection correcting table including the dependence of the surface height, which table is capable of keeping up with the drift of the electron beam or the like, can be accurately obtained without reducing the throughput.

FIELD OF THE INVENTION

The present invention relates to a workpiece holder for holding aworkpiece such as a semiconductor wafer, a semiconductor fabricatingapparatus having the workpiece holder, a semiconductor inspectingapparatus, a circuit pattern inspecting apparatus, a charged particlebeam application apparatus, a calibrating substrate, a workpiece holdingmethod, a circuit pattern inspecting method, and a charged particle beamapplication method.

BACKGROUND OF THE INVENTION

With the trend toward finer-geometries of circuit-patterns ofsemiconductor wafers, a circuit pattern inspecting apparatus employingelectron beams has come to be put into practical use.

Techniques concerning such a circuit pattern inspecting apparatus havebeen described, for example, in Japanese Patent Laid-open No. Sho59-192943, Japanese Patent Laid-open No. Hei 05-258703, Sandland, etal., “An electron-beam inspection system for x-ray mask production”, J.Vac. Sci. Tech. B, Vol.9, No.6, pp.3005-3009 (1991), Meisburger, et al.,“Requirements and performance of an electron-beam column designed forx-ray mask inspection”, J. Vac. Sci. Tech. B, Vol.9, No.6, pp.3010-3014(1991), Meisburger, et al., “Low-voltage electron-optical system for thehigh-speed inspection of integrated circuits”, J. Vac. Sci. Tech. B,Vol.10, No.6, pp.2804-2808 (1992), Hendricks, et al., “Characterizationof a New Automated Electron-Beam Wafer Inspection System”, SPIE Vol.2439, pp.174-183 (Feb. 20-22 1995).

To inspect a circuit pattern, which comes to be formed infiner-geometries on a wafer having an increased diameter, highlyaccurately at a high throughput, it is necessary to acquire a patternimage with a higher SN ratio at a very higher speed. To satisfy such arequirement, it is required to keep a higher SN ratio by ensuring thenecessary number of electrons to be emitted to the circuit pattern usinga large current beam which is equal to or more than 100 times (10 nA ormore) that used for a usual scanning electron microscope (SEM), andfurther, it is essential to highly efficiently detect secondaryelectrons produced from a substrate and reflection electrons reflectedtherefrom at a higher speed.

On the other hand, to prevent a semiconductor substrate having aninsulating film such as a resist from being affected by electrification,the semiconductor substrate is irradiated with a low accelerationelectron beam of 2 KeV or less. The technique is described on pages622-623 in “Electron and Ion Beam Handbook” 2nd Edition, edited by 132ndcommittee of Japan Society for the Promotion of Science, published byNikkan Kogyo Simbun, Ltd. (1986). A large current and low accelerationelectron beam, however, makes it difficult to observe a circuit patternat a high resolution because it produces aberration due to thespace-charge effect.

A method of solving such a problem has been known in which a highacceleration electron beam is retarded directly before a workpiece toirradiate the workpiece with a substantially low acceleration electronbeam. The technique has been described, for example, in Japanese PatentLaid-open Nos. Hei 02-142045 and Hei 06-139985.

The outline of one example of an electro-optical system of a prior artcircuit pattern inspecting apparatus will be described below withreference to FIG. 9. FIG. 9 is a schematic view of an electro-opticalsystem of the prior art circuit pattern inspecting apparatus.

A primary electron beam 201 emitted from an electron gun 1 with avoltage applied to an extraction electrode 2 passes through a condenserlens 3, a scanning deflector 5, an aperture 6, an objective lens 9 andthe like to be converged and deflected onto a substrate 10 for asemiconductor device placed on workpiece stages 11 and 12. To retard theprimary electron beam 201, a retarding voltage is applied from a highvoltage power source 23 to the substrate 10. The irradiation of thesubstrate 10 with the primary electron beam 201 produces secondaryelectrons 202 from the substrate 10. The secondary electrons 202 areaccelerated to an energy of several KeV by the retarding voltage. An EXBdeflector 8 is provided on the electron gun side of the objective lens 9in such a manner as to be adjacent to the objective lens 9.

The EXB deflector 8 is adapted to cancel the deflection amounts of theprimary electron beam 201 due to an electric field and a magnetic fieldeach other and to deflect the secondary electrons 202 by superimpositionof the deflection amounts of the secondary electrons 202 due to theelectric field and magnetic field. The accelerated secondary electrons202 thus deflected by the EXB deflector 8 is attracted by an electricfield formed by an attraction voltage applied between a detector 13 andan attraction electrode 14 mounted around the detector 13, to enter thedetector 13.

The detector 13 is configured as a semiconductor detector. The secondaryelectrons 202 having entered the semiconductor detector produceelectron-positive hole pairs which are then taken out as a current to beconverted into an electric signal. The output signal is amplified by apre-amplifier 21, to become a brilliance modulation input for forming animage signal. After an image of one region of the substrate is acquiredby the above operation of the electro-optical system, the image outputsignal is delayed for a time corresponding to one image plane, and thenan image of a second region is similarly acquired. These two images arecompared with each other by an image comparing/evaluating circuit, tothus detect a defective portion of the circuit pattern. Here, theirradiated position with the primary electron beam 201 is determined asa position of the substrate on which the electron beam is impinged onthe basis of a scanning-deflection signal inputted in the scanningdeflector 5.

If the surface height of the substrate is varied by warping of the waferor the like, however, the irradiated region of the substrate with anelectron beam is substantially varied although the electron beam isscanned on the basis of the same deflection signal, that is, the samebeam deflection cannot be obtained between two irradiated regions of thesubstrate.

To solve such a problem, a prior art electron beam application apparatussuch as an electron beam plotting apparatus has adopted the followingdeflection correcting manner:

(1) A sample with standard marks formed on at least two surfacesdifferent in thickness is provided at the outermost peripheral portionof a workpiece stage, and a positional offset between image signalsobtained from the standard marks having the different heights iscalculated.

(2) The height of each standard mark is converted into a signal byoperating an optical sensor for successively measuring the surfaceheight of the workpiece.

(3) A deflection correcting table corresponding to the height iscalculated on the basis of the height signal of each standard mark andthe positional offset between image signals of the standard marks. Thedeflection correcting table is stored, and upon observation of thesubstrate, the deflection is corrected by calculating a deflectioncorrecting signal corresponding to the surface height of the substrateon the basis of the deflection correcting table.

With this technique, even if the surface height of a substrate is variedby warping of the wafer or the like, two regions of the substrate whichare different in surface height can be equally irradiated with anelectron beam on the basis of a corrected deflection signal.

The technique has been described, for example, in Japanese PatentLaid-open No. Sho 56-103420. According to this technique, the deflectioncorrecting table can be simply updated by repeatedly observing thestandard marks provided at the(outer peripheral portion of the workpiecestage on which the wafer is left mounted. As a result, even if thereoccurs a drift of the deflection amount of a primary electron beam dueto the change in the electro-optical system with the elapsed time, thedeflection can be corrected in such a manner as to keep up with thechange with the elapsed time by re-observing the standard marks aboutseveral ten times at a specific period of time during processing of onewafer, and updating the deflection correcting table for eachre-observation.

A circuit pattern inspecting apparatus adopting the above-describeddeflection correcting method, however, has been not realized so far.

The gist of the present invention is to provide a circuit patterninspecting apparatus adopting the above-described deflection correctingmethod for coping with the warping of a wafer. However, if the circuitpattern inspecting apparatus adopts the above deflection correctingmethod as it is, there occurs the following problems:

Since a retarding voltage is applied to a substrate, a primary electronbeam is affected by an electric field caused by the retarding voltagedirectly before reaching the substrate.

In general, since a change in electric field is distributedaxisymmetrically with respect to the central axis of the primaryelectron beam, the primary electron beam can be deflected to a desiredregion by uniformly adjusting the deflection sensitivity irrespective ofthe position of the wafer. However, at the outer peripheral portion ofthe wafer, there is produced a nonaxisymmetric disturbance of anelectric field caused by the retarding voltage due to the sectionalshape of the wafer itself and the sectional structure of an end portionof the workpiece stage on which the water is mounted.

In the circuit pattern inspecting apparatus, since a signal is obtainedby one large current scanning only, a retarding voltage being as high asseveral times or more that used for another electron beam applicationapparatus is required to restrict the beam diameter into a desired valueand to allow a low acceleration electron beam to be impinged on thesubstrate. Accordingly, the amount of change in electric field caused bythe retarding voltage becomes larger than that for another electron beamapplication apparatus.

As a result, depending on whether or not an observation region of thesubstrate, that is, an irradiated region with a primary electron beam islocated near the outer peripheral portion of the wafer, there occurs anunnegligible difference of the beam, called “beam deflection”, betweenthe two irradiated regions located near the outer peripheral portion andin the central portion of the wafer although these regions areirradiated with the primary electron beam on the basis of the samedeflection signal.

In such circumstances, even if a deflection correcting table is preparedby providing, like another electron beam application apparatus, standardmarks formed on at least two surfaces different in thickness at theoutermost peripheral portion of a workpiece stage, the deflectioncorrecting table is affected by the beam distortion inherent to theouter peripheral portion of the workpiece stage. As a result, a suitabledeflection correcting signal for the associated position cannot beobtained by referring to the deflection correcting table on the basis ofthe measurement result of the surface height of the workpiece at thecentral portion of the workpiece stage, giving rise to a problem inwhich there occurs a deviation in irradiated position with the electronbeam.

The deviation in irradiated position with the electron beam leads to adeviation in pixel in an image signal obtained from the deviatedposition, thereby causing degradation of the accuracy in comparativeinspection of the images. If the deviation in pixel exceeds a specificallowable range, there occurs a problem that the inspection accuracy iscritically degraded in the circuit pattern inspecting apparatus aimed atcomparative inspection of images.

On the other hand, of a semiconductor fabricating apparatus and asemiconductor inspecting apparatus, an electron beam applicationapparatus for processing a workpiece by irradiating a workpiece with anelectron beam or inspecting the workpiece using an electron beam isrequired to emit an electron beam in vacuum. Further, to improve theprocessing accuracy of a workpiece or improving the resolution of animage obtained upon inspection, it is required to control theirradiation energy intensity of the emitted electron beam.

In recent years, the electron beam application apparatus such as anelectron beam plotting apparatus for processing a pattern of asemiconductor by irradiating it with an electron beam, a lengthmeasuring SEM (scanning electron microscope) for measuring a width orthe like of a pattern on the surface of a semiconductor, or an analyzingSEM for analyzing the material of a semiconductor by irradiating thesemiconductor with an electron beam, has adopted a retarding method ofapplying a voltage to a workpiece for controlling the irradiation energyintensity of an electron beam. The technique has been described, forexample, in Japanese Patent Laid-open Nos. Hei 05-258703 and Hei06-188294.

However, a workpiece holder used for the electron beam applicationapparatus such as a length measuring SEM or analyzing SEM has failed tocope with a variation in electric field caused at an end portion of aworkpiece due to a retarding voltage applied to the substrate. As aresult, if it is intended to irradiate an end portion of a workpiecewith an electron beam, the accuracy of the relationship between theirradiated position with the electron beam and the actual workpieceposition is significantly degraded due to a variation in electric field,so that there occurs a problem that a portion near the end portion ofthe workpiece cannot be processed, analyzed or inspected.

SUMMARY OF THE INVENTION

A first object of the present invention is to solve the above problemsof the prior art and to highly fast, stably acquire highly accurateimages from irradiated positions with an electron beam on a circuitpattern at the step of fabricating a semiconductor device including aninsulating material or a mixture of an insulating material and aconductive material, without occurrence of any deviation in theirradiated position in the images to be comparatively inspected,automatically comparing the images with each other thereby inspectingdefects of the circuit pattern without occurrence of errors, and feedingback the result to the conditions of fabricating the semiconductordevice thereby increasing the reliability of the semiconductor deviceand reducing the defective percentage thereof.

As a means for achieving the above object, a typical example of acircuit pattern inspecting apparatus of the present invention will bedescribed.

The circuit pattern inspecting apparatus of the present inventionbasically includes an irradiation optical system for converging aprimary charged particle beam while deflecting the primary chargedparticle beam so as to scan first and second regions of a circuitpattern of a workpiece with the primary charged particle beam; aretarding/accelerating means for retarding the primary charged particlebeam, and accelerating secondary charged particles produced from theworkpiece by the irradiation of the workpiece with the primary chargedparticle beam and reflection electrons reflected from the workpiece; aworkpiece stage for holding the workpiece; a sensor for measuring thesurface height of an irradiated position of the workpiece with theprimary charged particle beam; a detector for detecting the secondarycharged particles produced from the workpiece; and an image formingmeans for forming an image of the irradiated region of the workpiecefrom a signal detected by the detector. The apparatus further includesan outer peripheral sample having outer peripheral standard marks formedon at least two surfaces different in thickness in the direction of theaxis of the primary charged particle beam, the outer peripheral samplebeing provided at an outer peripheral portion of a substrate mountingarea of the workpiece stage; a central sample having central standardmarks formed on at least two surfaces different in thickness in thedirection of the axis of the primary charged particle beam, the centralsample being provided at a central portion of the substrate mountingarea of the workpiece stage; a storing means for storing image signalsobtained from the outer peripheral standard marks of the outerperipheral sample and the central standard marks of the central sample;a computing means for computing a distortion amount of the primarycharged particle beam inherent to the outer peripheral portion from theouter peripheral and central standard mark image signals; an eliminatingmeans for eliminating the distortion amount inherent to the outerperipheral portion from the outer peripheral standard mark imagesignals; a storing means for preparing a deflection correcting table inaccordance with the height of the workpiece on the basis of the outerperipheral standard mark image signals from which the distortion amounthas been eliminated, and storing the deflection correcting table; adeflection correcting signal generating circuit for taking out adeflection correcting signal from the deflection correcting table inaccordance with the surface height signal obtained by the sensor; and acontrol means for controlling to irradiate the outer peripheral samplehaving the outer peripheral standard marks at a desired timing to updatethe deflection correcting table.

In addition, preferably, a shield electrode is provided in the vicinityof the above substrate to reduce the disturbance of the electric fieldcaused by a retarding voltage.

The function of the circuit pattern inspecting apparatus and circuitpattern inspecting method will be described below. The above circuitpattern inspecting apparatus compares the dependence of the workpieceheight on the corrected amount of deflection at the central portion ofthe workpiece stage with that at the outer peripheral portion of aworkpiece, to obtain a distortion amount inherent to the outerperipheral portion of the workpiece. Then, the dependence of height onthe corrected amount of deflection at the outer peripheral portion ofthe workpiece is calculated by eliminating the distortion amountinherent to the outer peripheral portion from the standard mark signalof the outer peripheral portion, to obtain a deflection correctingamount at the outer peripheral portion which is equivalent to thedeflection correcting amount obtained at the central portion.

Further, since a suitable deflection correcting table can be preparedonly on the basis of the standard mark at the outer peripheral portion,the deflection correcting table can be updated by repeating desiredtimes the calculation of the deflection correcting amount at the outerperipheral portion while holding the wafer on the workpiece stage. As aresult, the deflection correcting table including the dependence ofsurface height, which is capable of keeping up with the drift of theelectron beam, can be accurately obtained without reducing thethroughput.

On the other hand, at the outermost peripheral portion of a wafer, thereexists a region in which the deflection cannot be corrected on the basisof the same correcting table to produce the positional deviation, and ifthe result of image comparison at the region is outputted, there is apossibility that a large number of misdetections occur. For this reason,the present invention is configured such that the inspection is notperformed in a region in which the deflection cannot be corrected on thebasis of the same correcting table. This allows highly accurateinspection with no misdetection.

The provision, in the vicinity of the workpiece, of a shield electrodehaving the same potential as the retarding voltage of the workpiece hasmakes it possible to reduce the disturbance of an electric field nearthe workpiece, and hence to more extend a region on the wafer in whichdeflection can be corrected on the basis of the same correcting table.

According to the circuit pattern inspecting apparatus having the abovefunctions, it is possible to highly fast, stably acquire highly accurateimages from irradiated positions with an electron beam on a circuitpattern at the step of fabricating a semiconductor device including aninsulating material or a mixture of an insulating material and aconductive material, without occurrence of any deviation in theirradiated position under a condition that a high retarding voltage isapplied to a substrate, and automatically comparing the images with eachother, thereby inspecting defects of the circuit pattern withoutoccurrence of errors.

A second object of the present invention is to provide an electron beamapplication apparatus having a function of controlling an electron beamirradiation energy with a retarding voltage, which is capable ofirradiating a position of a workpiece with an electron beam withoutreducing the accuracy of the irradiated position.

An electron beam application apparatus includes a vacuum chamber inwhich a workpiece such as a semiconductor device is irradiated with anelectron beam, a loader for carrying the workpiece in the vacuumchamber, a movable stage for allowing the workpiece to be mountedthereon and adjusting an irradiated position with the electron beam, aworkpiece holder disposed between the stage and the workpiece forholding the workpiece, a power source for applying a retarding voltageto the workpiece, a position measuring device for measuring the movedamount or the position of the stage, an electron source and a deflectorfor irradiating the workpiece with an electron beam for processing orobserving the workpiece, and an information processing device forobserving, analyzing, or inspecting the workpiece by making use ofinformation obtained by detecting reflection electrons or secondaryelectrons produced from the workpiece. The height of a boundary portionbetween a portion, on the electron beam incident side, of the workpieceholder and the workpiece is set to be substantially equal to the heightof the workpiece surface. With this configuration, since the electricfield distribution of the workpiece surface is nearly uniform up to theend portion of the workpiece, a variation in electric field caused bythe retarding voltage can be prevented. As a result, it is possible toirradiate the entire surface with an electron beam without reducing thepositional accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing the configuration of acircuit pattern inspecting apparatus according to the present invention;

FIG. 2 is a plan view showing a state in which a substrate to beinspected is mounted in the circuit pattern inspecting apparatus;

FIGS. 3A and 3B are electric field distribution diagrams each showingthe result of simulation of an inner electric field;

FIG. 4 is a typical diagram illustrating an electron trajectory;

FIG. 5 is a graph showing a relationship between extension of anirradiated position with an electron and a target deflected position;

FIG. 6 is a flow chart illustrating an operational procedure of thecircuit pattern inspecting apparatus according to the present invention,in which the plan view of a substrate to be inspected is additionallyshown;

FIG. 7 is a typical diagram showing one example of image display;

FIG. 8 is a plan view showing a state in which a substrate to beinspected is mounted on a workpiece stage;

FIG. 9 is a vertical sectional view showing the configuration of a priorart circuit pattern inspecting apparatus;

FIG. 10 is a vertical sectional view of essential components of asemiconductor inspecting apparatus using an electron beam;

FIG. 11 is a perspective view, with parts partially cutaway, showing theconfigurations of a workpiece stage and a workpiece holder of asemiconductor inspecting apparatus using an electron beam;

FIGS. 12A and 12B are a plan view and a vertical sectional view of aworkpiece holder shown in FIG. 2, respectively;

FIG. 13 is a plan view of another workpiece holder, in which thecross-section thereof is additionally shown;

FIG. 14 is a plan view of a prior art workpiece holder, in which theside view thereof is additionally shown;

FIGS. 15A, and 15B and 15C are a plan view and sectional views showingthe workpiece holding configuration of another prior art workpieceholder, respectively;

FIG. 16 is an electric field distribution diagram showing the result ofsimulation of an electric field distribution of a workpiece along thevertical cross-section of the workpiece surface;

FIG. 17A and 17B are electric field distribution diagrams each showingthe result of simulation of an electric field distribution of aworkpiece along the vertical cross-section of the workpiece surface; and

FIG. 18A and 18B are electric field distribution diagrams each showingthe result of simulation of an electric field distribution of aworkpiece along the vertical cross-section of the workpiece surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

First, embodiments of a circuit pattern inspecting apparatus, a circuitpattern inspecting method, and a calibration substrate according to thepresent invention will be described with reference to FIGS. 1 to 8.

First Embodiment

A circuit pattern inspecting apparatus according to one embodiment ofthe present invention will be described with reference to FIGS. 1 to 7.

One basic conception of the circuit pattern inspecting apparatusaccording to this embodiment is to accurately inspect a circuit patternby using a deflection correcting table which is optimized in a regionbeing as wide as possible by taking into account a disturbance of anelectric field due to a retarding voltage applied to a substrate as ahigh negative potential, which disturbance of an electric field appearsalong sectional shapes of outer peripheral portions of the substrate anda workpiece stage.

Another basic conception of the circuit pattern inspecting apparatus isto provide an electrode for flattening the disturbance of an electricfield caused by retarding voltage, thereby making small thecorrection-disable region to a degree negligible from the viewpoint ofthe practical use.

FIG. 1 is a vertical sectional view showing the configuration of thecircuit pattern inspecting apparatus of the present invention. Thecircuit pattern inspecting apparatus in this embodiment will bedescribed in detail with reference to FIG. 1. The circuit patterninspecting apparatus basically includes an electro-optical system 101, aworkpiece chamber 102, a control unit 103, and an image processing unit104.

The electro-optical system 101 is composed of an electron gun 1, anelectron beam extraction electrode 2, a condenser lens 3, a scanningdeflector 5, an aperture 6, a shield pipe 7, an EXB deflector 8, anobjective lens 9, an earth electrode 15, and a shield electrode 16.

The workpiece chamber 102 is composed of an X-Y stage 11, a rotatingstage 12, an optical height measuring device 26, and a length measuringdevice 27 for monitoring a position to be irradiated. A secondaryelectron detector 13 is located under the objective lens 9, and anoutput signal from the secondary electron detector 13 is amplified by apre-amplifier 21 and is then processed into digital data by an ADconvertor 22.

The image processing unit 104 is composed of an image storing units 30 aand 30 b, a computing unit 33, and a defect decision unit 34. Theelectron beam image and optical image incorporated in the imageprocessing unit 104 are displayed on a monitor 32.

An operational command and operation condition for each unit of thecircuit pattern inspecting apparatus are inputted/outputted in/from thecontrol unit 103. Various conditions upon generation of the electronbeam, such as an acceleration voltage, deflection width of an electronbeam, deflection speed, moving speed of a workpiece stage, and signalincorporation timing of the detector, are previously inputted in thecontrol unit 103.

A correction signal is created from signals supplied from the opticalheight measuring device 26 and length measuring device 27 for monitoringa position to be irradiated. Such a correction signal is fed to a powersupply 25 for the objective lens 9 and a scanning signal generator 24via a correction control circuit 28 in order that an electron beam 210is usually impinged on a correct position.

The electron gun 1 employs a thermal field emission electron source of adiffusion supply type, which allows creation of images less variation inbrightness to be comparatively inspected and which allows high speedinspection because the gun can increase an electron beam current.

The electron beam 201 is extracted from the electron gun 1 by applying avoltage to the extraction electrode 2. The acceleration of the electronbeam 201 is performed by applying a high negative voltage to theelectron gun 1. The electron beam 201 with an energy equivalent to thepotential applied thereto, for example, 12 keV in this embodimentadvances toward the workpiece stage 11, and is converged through thecondenser lens 3 and further finely restricted through the objectivelens 9, to be thus impinged on a substrate 10 to be inspected (forexample, wafer or chip) mounted on the X-Y stage 11.

A negative voltage, that is, a retarding voltage can be applied from ahigh voltage power source 23 to the substrate 10. The earth electrode 15is provided between the substrate 10 and the EXB deflector 8 to form anelectric field caused by retarding voltage between the earth electrode15 and the substrate 10. It is easy to adjust an electron beam energy tobe emitted to the substrate 10 at the optimum value by controlling thehigh voltage power source 23 connected to the substrate 10.

In this embodiment, a negative potential of −11.5 kV as the retardingvoltage is applied to the substrate 10. The formation of an image isperformed in accordance with either a method of two-dimensionallyscanning the electron beam 201 while allowing the X-Y stage 11 to remainat rest or a method of one-dimensionally scanning the electron beam 201and continuously moving the X-Y stage 11 in the direction substantiallyperpendicular to the scanning direction.

In the case of inspecting only a specific location of the substrate 10,the inspection can be efficiently performed in accordance with theformer method in which the stage 11 remains at rest, while in the caseof inspecting a wide region of the substrate 10, the inspection can beefficiently performed in accordance with the latter method in which thestage 11 is continuously moved.

A surface image of the substrate 10 is acquired by irradiating thesubstrate 10 with the finely restricted electron beam 201 to producesecondary electrons 202, and detecting the secondary electrons 202 insynchronization with the scanning of the electron beam 201 and themovement of the stage 11.

The automatic inspection performed in this embodiment is essential tomake fast the inspecting speed, and accordingly, such automaticinspection does not adopt the scanning at a low speed with a beamcurrent of the pA order or the scanning repeated by a plurality oftimes, which scanning has been adopted in a usual SEM. That is to say,in the automatic inspection performed in this embodiment, an image isformed by only one scanning of a large current electron beam being equalto or more than about 100 times that used for the usual SEM, forexample, 100 nA.

A unit image for 1000×1000 pixels is acquired as a first image at a rateof 10 msec, and the second image is acquired on the basis of an imagesignal which is delayed for a time equivalent to one image. That is tosay, the second image is incorporated in synchronization with the firstimage. Both the images are then comparatively evaluated to thus search adefect on the substrate 10.

FIG. 2 is a plan view showing a state in which the substrate is mountedon the circuit pattern inspecting apparatus, and FIGS. 3A and 3B areelectric field distribution diagrams each showing the result ofsimulation of an inner electric field of the circuit pattern inspectingapparatus. The substrate 10 is mounted on the workpiece stage 11. When aretarding voltage is applied to the substrate 10 mounted as shown inFIG. 2, there occurs an electric field caused by retarding voltage alongthe shape of the substrate 10 as shown in FIGS. 3A and 3B.

Referring to FIG. 2, four projections C₁, C₂, C₃ and C₄ provided on theworkpiece stage 11 in such a manner as to surround the periphery of thesubstrate 10, wherein one projection C₁ of these projections isconfigured to be movable via a spring. The surface of the substrate 10is regarded as flattened in the macroscopic view, and as shown in FIG.3A, when the central portion of the substrate 10 is observed, it mayhave an electric field distribution with no disturbance.

On the contrary, at the outer peripheral portion of the substrate 10, asshown in FIG. 2, the sectional shape of the substrate 10 itself isuneven and also the projections C₁, C₂, C₃ and C₄ functioning assubstrate pressers are provided, and accordingly, as shown in FIG. 3B,an electric field is disturbed around the projections C₁, C₂, C₃ and C₄.Here, by the effect of the shield electrode 16 provided between theworkpiece 10 and the earth electrode 15, the disturbance of an electricfield caused by retarding voltage is reduced. The beam 201 is affectedby such an electric field distribution as follows:

FIG. 4 is a diagram illustrating the trajectory of the primary electronbeam 201, and FIG. 5 is a graph showing a relationship between theextension of an actual irradiated position with the primary electronbeam 201 and a target deflected position. As shown in FIG. 4, theprimary electron beam 201 is not impinged on the workpiece 10 along alinear trajectory from an intersection between a beam axis and adeflected beam, so-called deflection fulcrum (not shown) but it isretarded from a high acceleration state as nearing the vicinity of theworkpiece 10 and is impinged on the workpiece 10 while being veryslightly extended from the linear trajectory by the effect of theaxisymmetric deflection action of the electric field caused by theretarding voltage. In the case where the beam 201 is impinged on thecentral portion of the substrate 10, assuming that the surface of thesubstrate 10 is substantially flattened in a macroscopic view, it issufficient for only the above axisymmetric extension to be taken intoaccount.

Referring to FIG. 4, in the case of irradiation of the central portionof the substrate 10, the primary electron beam 201 reaches an irradiatedposition x1 linearly shifted from a predetermined irradiated position x0on the basis of a deflection signal. The irradiated position x1 becomesa value corresponding to the surface height of the workpiece 10 as shownin FIG. 5.

On the contrary, in the case of irradiation of the outer peripheralportion of the substrate 10, the beam 201 is further deflected by thedisturbance of the neighborhood electric field caused along thesectional shape of the substrate 10. As shown in FIG. 5, uponobservation of the outer peripheral portion, the beam 201 reaches anirradiated position x2 which is shifted from the irradiated position x1substantially in parallel to one direction on the substrate 10. Theshifted amount (x2-x1) is equivalent to a beam distortion amount, whichis dependent on the sectional shape of the portion, in the vicinity ofthe irradiated position, of the substrate 10.

As a result of examination, it becomes apparent that the shifted amount(x2-x1) can account for about several tens % of the deflection width ofthe beam, and that the beam distortion amount (x2-x1) is, strictlyspeaking, not linearly changed from the predetermined irradiatedposition. The fact that the beam distortion amount at the outerperipheral portion of the substrate is the non-linear and non-negligibleamount causes the following two problems:

One problem is that both the correction upon observation of the outerperipheral portion and the correction upon observation of the centralportion cannot be performed using the same correction table. Anotherproblem is that if a standard mark sample for preparing a deflectioncorrection table is provided at the outer peripheral portion of theworkpiece stage 11, the prepared correction table itself contains thedistortion amount of the primary electron beam 201, with a result thatthe deflection cannot be suitably corrected using such a deflectioncorrection table.

Additionally, in this circuit pattern inspecting apparatus which isaimed at automatically, relatively inspecting images at a high speed, itis required to prepare a deflection correction table for a short periodof time while keeping up with the beam drift due to a change in theelectro-optical system 101 with the elapsed time.

To be more specific, the circuit pattern inspecting apparatus accordingto the present invention is adapted to relatively inspect images whilecorrecting deflection of an electron beam in accordance with a procedureshown in FIG. 6. FIG. 6 is a flow chart illustrating the operationalprocedure for the circuit pattern inspecting apparatus, in which theplan view of a substrate to be inspected is additionally shown. First, abasic calibration flow is executed upon periodical maintenance of thecircuit pattern apparatus.

A calibrating wafer in which a sample with standard marks formed on twosurfaces different in thickness (+200 μm, −200 μm) is buried is loadedon the central portion of the workpiece stage 11, and images at thesurface heights zH and zL of the central standard marks are acquired.The image signals thus obtained are stored in a central standard marksignal storing unit 35. The range of each of the surface heights zH andzL of the standard marks is set at a value nearly equal to a variationrange of the surface height of the substrate 10 caused by warping of thesubstrate 10. Next, a sample 17 with standard marks formed on twosurfaces different in thickness is similarly provided at the outermostperipheral portion of the workpiece stage, and images therefrom areacquired and stored in an outer peripheral standard mark signal storingunit 36.

The standard mark image signals thus obtained in accordance with thepresent invention are shown in FIG. 7. FIG. 7 is a typical diagramshowing one example of image indication.

As shown in FIG. 7, a true configuration of the standard mark [xk], acentral standard mark signal [x3] and an outer peripheral standard marksignal [x2] form different mark images, respectively. The signals readfrom the storing unit 35 in which the central standard mark signal [x3]is stored and from the storing unit 36 in which the outer peripheralstandard mark signal [x2] is stored are converted into a distortioncoefficient [B] by a comparing unit 37. That is to say, an outerperipheral distortion coefficient B is calculated from a positionaldeviation between the central and outer peripheral standard mark signalsand is stored in an outer peripheral distortion amount storing unit 38.

The outer peripheral distortion coefficient B is defined by thefollowing equations (1) and (2).

[x 2(zH)]=[B(zH)][x 3(zH)]  (1)

[x 2(zL)]=[B(zL)][x 3(zL)]  (2)

While the outer peripheral distortion amount B upon periodicalmaintenance is stored, the next calibration flow based on the outerperipheral standard marks is carried out for each wafer. Like the basiccalibration, images of a sample with standard marks formed on twosurfaces having heights zH and zL provided at the outermost peripheralportion of the workpiece stage are formed. The absolute value of thedifference between zH and zL, (|zH−zL |) is set at 400 μm.

The positional signals of the outer peripheral standard marks [x2(zH)]and [x2(zL)] are stored in the storing unit 36. An outer peripheraldeflection distortion coefficient C is calculated by comparing the outerperipheral standard mark signal [x2] with the true position xk of thestandard mark using a computing circuit 39 for removing the outerperipheral distortion amount.

The outer peripheral deflection distortion coefficient C is defined bythe following two equations (3) and (4): $\begin{matrix}\begin{matrix}{\left\lbrack {{x2}\left( {z\quad H} \right)} \right\rbrack = {\left\lbrack {C\left( {z\quad H} \right)} \right\rbrack \quad\lbrack{xk}\rbrack}} \\{= {\left( {\left\lbrack {A\left( {z\quad H} \right)} \right\rbrack + \left\lbrack {B\left( {z\quad H} \right)} \right\rbrack} \right)\quad\lbrack{xk}\rbrack}}\end{matrix} & (3) \\\begin{matrix}{\left\lbrack {{x2}\left( {z\quad L} \right)} \right\rbrack = {\left\lbrack {C({zL})} \right\rbrack \quad\lbrack{xk}\rbrack}} \\{= {\left( {\left\lbrack {A({zL})} \right\rbrack + \left\lbrack {B({zL})} \right\rbrack} \right)\quad\lbrack{xk}\rbrack}}\end{matrix} & (4)\end{matrix}$

The above distortion amount contains a distortion amount inherent to theouter peripheral portion because the standard mark is positioned at theoutermost peripheral portion of the workpiece stage.

The distortion amount [B] caused only at the outer peripheral portion,which is obtained by the difference between the outer peripheralstandard mark signal and the central standard mark signal on the basisof the above equations (1) and (2), is substituted in the aboveequations (3) and (4), to eliminate the outer peripheral distortioncoefficient [B], thereby obtaining a deflection distortion coefficient[A] equivalent to the central distortion amount.

The deflection distortion coefficient [A] is defined by the followingequations (5) and (6):

[A(zH)]=[C(zH)]−[B(zH)]  (5)

[A(zL)]=[C(zL)]−[B(zL)]  (6)

The deflection distortion coefficient [A] has been obtained from aspecific height, that is, each of the standard marks formed on the twosurfaces of the workpiece, and accordingly, a specific deflectioncorrecting table can be calculated on the basis of the deflectiondistortion coefficient [A], and further a general deflection correctingtable for an arbitrary height can be calculated by a storing unit 40.

Assuming that the height dependency of the general deflection correctingtable is linear, the general deflection correcting table can be obtainedfor each height using a so-called interpolation method.

 [A(z)]=([A(zH)]−[A(zL)])×(z−zL)/[(zH−zL)]+[A(zL)]

In this way, by the above two-stage calibration of the deflectioncorrecting table, the highly accurate deflection correcting table notaffected by the beam distortion can be updated without frequentlyperforming the basic calibration flow requiring replacement of thesubstrate 10 and taking a long period of time.

After the deflection correcting table is accomplished by the calibrationflow described above and is stored, the usual inspection begins.

First, a region to be inspected of the substrate 10 is successivelymeasured by the workpiece height measuring device 26, and height signalsare fed to a deflection correcting signal generating circuit 29. Thecircuit 29 creates a deflection correcting signal while referring to thedeflection correcting table. The beam 201 is deflected on the basis ofthe deflection correcting signal, to take out an image signal. The imagesignals thus taken out are processed by a delay circuit 31 such that thefirst image signal is delayed from the second one for a time equivalentto one image, and are compared with each other by the computing unit 33.The presence or absence of a defect is decided by the defect decisionunit 34 on the basis of the compared result. In this embodiment, toallow the deflection correcting table to highly accurately keep up withthe drift of the beam 201 caused by a change in the electro-opticalsystem 101 with the elapsed time, the observation of the image of outerperipheral standard mark 17 and the update of the deflection correctingtable are carried out at one timing for each wafer by an update controlunit 41 for updating the deflection correcting table.

A. new outer peripheral mark signal and the existing outer peripheraldistortion amount are computed, and a deflection correcting table isupdated by eliminating the distortion amount. The updating timing of thedeflection correcting table can be previously set in the update controlmeans 41.

Further, in this embodiment, as shown in FIG. 6, a region of thesubstrate 10 narrower than the outer periphery by a width of 10 mm isdecided as a region in which deflection cannot be corrected using thesame deflection correcting table, that is, as an inspection disable areaby an inspection unavailable region control means 42. That is to say,the decision for such a region is regarded as unavailable by the defectdecision unit 34, and such a region is not irradiated with the electronbeam 201.

The reason for this is that since the workpiece stage 11 has theanisotropic configuration in which the beam distortion is uneven, thecorrection in consideration of the dependence of the position of thesubstrate on the correcting table becomes very complicated and takes alot of time.

The width of the sample with the outer peripheral standard marks is setat 10 mm in consideration of a range in which the beam can be correctedusing the same deflection correcting table, and an image is acquired atthe center of the sample surface at each height of the standard mark.The sample with the central standard marks is configured to be larger inits area than the sample with the outer peripheral standard marks, andthe image formation of each central standard mark is performed at aposition separated 10 mm or more than the boundary between the twosurfaces of the standard marks.

According to this embodiment, it is possible to reduce the misdetectionratio by 20% as compared with the case in which the inspection isperformed by correcting deflection not in consideration of the beamdistortion using the same electro-optical system.

In the above embodiment, description is made using the electron sourceand electron beam are used; however, in the case of using a chargedparticle source and charged particle beam, the same configuration asthat of the above electro-optical system is called an irradiationoptical system.

Second Embodiment

A circuit pattern inspecting apparatus according to another embodimentof the present invention will be described with reference to FIG. 8.

FIG. 8 is a plan view, similar to FIG. 2, showing a state in which asubstrate to be inspected is mounted on a workpiece stage. Thisembodiment is different from the first embodiment in that a workpiecestage 11 having an isotropic configuration is used, and accordingly,this embodiment will be described only with reference to the partialconfiguration view of FIG. 8. The workpiece stage 11 of an electrostaticchuck type is 100 μm or less higher than the surface of a substrate 10as the workpiece and wider 10 mm than the outer periphery of thesubstrate 10 in the moving direction.

A portion, having a center angle of 180° or more, of the workpiece stage11 located around the substrate 10 is movable, and after the substrateis mounted on the workpiece stage 11, the movable portion of theworkpiece 11 is moved in proximity to the substrate 10 and fixed at aposition in contact with the outer periphery of the substrate 10. Thisconfiguration is complicated and is hard in actual operation, but isadvantageous in that the beam distortion caused at an end portion of thesubstrate 10 is reduced, thereby making it possible to inspect thenearly entire surface of the substrate 10, for example, a range havingan outer limit positioned 3 mm inwardly from the outer periphery of thesubstrate 10. In this embodiment, it is not required to generate anunavailable signal from the inspection unavailable region control means42.

Third Embodiment

A further embodiment of the present invention will be described below.In this embodiment, while not shown, the inside diameter of the shieldelectrode 16 is reduced to half, that is, changed from 30 mm Φ to 15 mmΦ. As a result, the disturbance of an electric field caused by aretarding voltage is reduced. This makes it possible to inspect a rangehaving an outer limit positioned 7 mm inwardly from the outer peripheryof the substrate 10.

As described above, according to the present invention, there can beobtained the circuit pattern inspecting apparatus or circuit patterninspecting method of previously taking into account the disturbance ofan electric field caused in the vicinity of the outer peripheral portionof the substrate 10 as the workpiece to which a high negative retardingvoltage is applied, thereby highly accurately correcting the deflectionof the primary electron beam 201 in such a manner as to be matched withthe height of an irradiated position of the substrate 10 with theelectron beam 201 without receiving adverse effect of the distortion ofthe beam 201 at the outer peripheral portion of the substrate 10. In theabove apparatus or method, the deflection correcting table is preparedon the basis of the outer peripheral standard marks 17; however, theremay be adopted another configuration in which the diameter of theworkpiece stage 11 is made sufficiently larger than the size of thewafer and the standard marks 17 are provided inwardly from the outerperiphery of the workpiece stage 11 sufficiently to prevent occurrenceof the beam distortion.

The effect of the disturbance of an electric field is varied by changinga retarding voltage and thereby the inspection effective region isvaried. In consideration of such a change, the inspection unavailableregion control means 42 is provided. This enables inspection with lesswastage. In addition, the numeral values described in the aboveembodiments are for illustrative purposes only, and it is to beunderstood that the present invention may be of course carried out underdifferent specifications. For example, the circuit pattern can be moreefficiently, highly accurately inspected by optimizing the width andheight of each of the substrate pressing projection of the workpiecestage and substrate drop hole, and the thickness and size of theworkpiece with the standard marks in consideration of the conditionssuch as the size and thickness of the substrate, a variation range ofthe surface height of the substrate due to warping, and a retardingvoltage.

As described above, according to the present invention, even if a highlyretarding voltage is applied to a substrate as a workpiece, thedeflection of the primary electron beam can be highly fast, highlyaccurately corrected in such a manner as to be matched with the heightof the workpiece without receiving adverse effect of the beam distortioncaused at the outer peripheral portion of the substrate. As a result,with respect to a circuit pattern at the step of fabricating asemiconductor device including an insulating material or a mixture of aninsulating material and a conductive material, it is possible to highlyfast, stably acquire highly accurate images from desired positions ofthe circuit pattern by irradiating the positions with an electron beam,without occurrence of any deviation between the irradiated positions,and automatically comparing the images with each other, therebyinspecting defects of the circuit pattern without occurrence of errors.

Fourth Embodiment

A further embodiment of the present invention will be described below.

As one example of an electron beam application apparatus, asemiconductor inspecting apparatus using an electron beam will bedescribed. FIG. 10 is a vertical sectional view showing main parts ofthe semiconductor inspecting apparatus using an electron beam. Thesemiconductor inspecting apparatus inspects whether or not asemiconductor wafer or a circuit pattern formed on a circuit patternmask for transferring the circuit pattern on the wafer is desirablyprepared. Accordingly, in the semiconductor inspecting apparatus, awafer or mask is taken as a workpiece.

Referring to FIG. 10, an electro-optical system of the semiconductorinspecting apparatus includes an electron gun 502 for emitting electronswith electric power supplied from a power source 501; an electron beam503 extracted from the electron gun 502; a condenser lens 506 a and anobjective lens 506 b for converging the electron beam 503 so as toirradiate a wafer 510 as the workpiece with the electron beam 503; adeflector 511 for deflecting the electron beam 503 so as to irradiate adesired position of the wafer 510 with the electron beams 503; and amirror body 505 containing a secondary electron detector 515 fordetecting secondary electrons produced from the wafer 510 by irradiationof the wafer 510 with the electron beam 503 and a Wien filter 514 forchanging the direction of the secondary electrons toward the secondaryelectron detector 515. The values of currents applied to the deflector511 and objective lens 506 b are controlled by a control unit 513.

The wafer 510 is carried from a load lock chamber 519 into a workpiecechamber 507 and mounted on a workpiece holder 521 in the workpiecechamber 507 by a carrying unit 520. The position of the workpiece holder521 is fixed by pallet guides 526 of a movable stage 508. The mirrorbody 505 and workpiece chamber 507 are evacuated via exhaust units 504 aand 504 b and exhaust units 504 c and 504 d, respectively. A gate valve518 is provided between the load lock chamber 519 and workpiece chamber507, which gate valve 518 is opened only when the wafer 510 is carriedin the workpiece chamber 507.

Since the scanning range of the electron beam 503 by the deflector 511is narrower than the size of the wafer 510, the stage 508 iscontinuously or intermittently moved to allow a desired circuit patternof the wafer 510 to be irradiated with the electron beam 503. At thistime, the alignment of the wafer 510 is performed by measuring theposition of the stage 508 using a laser interferometer 512, andcorrecting the position of the wafer 510 by superimposing a correctedamount representative of the position of the stage 508 on the deflectedamount of the electron beam 503 by the control unit 513.

The secondary electrons produced from the wafer 510 by irradiation ofthe wafer 510 with the electron beam 503 are deflected toward thesecondary electron detector 515 by the Wien filter 514 and are detectedby the secondary electron detector 515. The detected amount of thesecondary electrons is amplified by an amplifier 516, being processed byan information processing unit 517, and is outputted as an image signalfrom the information processing unit 517.

To improve the resolution of an image of the secondary electrons, thevoltage applied to the electron beam 503 may be increased; however,depending on the kind of the workpiece, there may occur an inconveniencethat the workpiece is destroyed by the energy of the high voltageelectron beam 503. To cope with such an inconvenience, there is known amethod of retarding the electron beam 503 just before the workpiece byapplying a negative retarding voltage from a retarding power source 509to the workpiece. This method is particularly effective for inspecting aworkpiece such as a semiconductor wafer.

FIG. 11 is a perspective view, with parts partially cutaway, showing theconfigurations of the stage 508 and workpiece holder 521.

The workpiece holder 521 is fixed on the stage 508 while being guided bythe pallet guides 526. The wafer 510 is mounted on the workpiece holder521 via an electrostatically attracting unit 521 a. A holding plate 521b surrounds the wafer 510. The workpiece holder 521 is provided with acarrying port 531 through which the wafer 510 is transferred in or fromthe workpiece holder 521. The stage 508 is moved by drive rods 525 a and525 b in the directions along linear guides 527 a and 527 b.

FIGS. 12A and 12B are a plan view and a vertical sectional view of theworkpiece holder 521 shown in FIG. 11, respectively. FIG. 12A shows astate before the holding plate 521 b located around the wafer 510 ismoved, and FIG. 12B shows a state after the holding plate 521 b locatedaround the wafer 510 is moved.

Referring to FIG. 12A, the wafer 510 is carried into the workpieceholder 521 through the carrying port 531 and is mounted on theelectrostatically attracting unit 521 a. Then, as shown in FIG. 12B, thewafer 510 is lifted by a lifting mechanism 528 in the lifting direction536 up to a height being nearly equal to that of the holding plate 521b, so that the surface height of the wafer 510 becomes nearly equal tothat of the holding plate 521 b of the workpiece holder 521. Next, theholding plate 521 b divided into two or more parts is slid by a holdersliding mechanism 532 in the slide direction 535 toward the center ofthe wafer 510, to be brought in contact with an end portion of the wafer510. In this embodiment, the holding plate 521 b is divided into fourparts.

Although it may be desirable that the surface height of the wafer 510 beperfectly equal to that of the holding plate 521 b of the workpieceholder 521, it is difficult to make the surface height of the wafer 510perfectly equal to that of the holding plate 521 b from the viewpointsof machining accuracy, assembling accuracy and the like. Accordingly, itis required to set a dimensional tolerance with respect to theidentification between both the surface heights of the wafer 510 andholding plate 521 b, and such a dimensional tolerance has beenexperimentally found by the present inventors (which will be describedin detail later).

Although a slight gap 537 is set between the wafer 510 and holding plate521 b in this embodiment, it may be desirable not to be presenttherebetween. From the viewpoint of practical use, however, the gap 537may be formed therebetween depending on machining accuracies of theouter peripheral dimension of the wafer 510 and the dimension of theholding plate 521 b. The dimensional tolerance of such a gap will bedescribed later.

Fifth Embodiment

FIG. 13 is a plan view of a workpiece holder 521 as a further embodimentof the present invention, in which the vertical cross section of theworkpiece holder 521 is additionally shown. A wafer 510 is mounted on anelectrostatically attracting unit 521 a, and one of a plurality ofholding pins 539 is moved in the pin moving direction 540 to fix theposition of the wafer 510. Then, a holding plate 521 c is moved in thelifting direction 536, so that the surface height of the wafer 510becomes nearly equal to that of the holding plate 521 c.

FIG. 14 and FIGS. 15A to 15C show configurations of prior art workpieceholders. FIG. 14 is a plan view of the first prior art workpiece holder,in which the side view of the workpiece holder is additionally shown.

Referring to FIG. 14, a wafer 510 is mounted on a supporting stage 530fixed on a workpiece holder 521, and the position of the wafer 510 isfixed by a plurality of bearings 529. Accordingly, the height of theworkpiece holder 521 located around an end portion of the wafer 510 islower than that of the wafer 510 by an amount equivalent to thethickness of the wafer 510.

FIG. 15A, and FIGS. 15B and 15C are a plan view and sectional views ofthe second prior art workpiece holder, respectively. Referring to FIG.15A, a wafer 510 is mounted on an electrostatically attracting unit 521a fixed on a workpiece holder 521, and the position of the wafer 510 isfixed by a plurality of claws 523 a. The cross-section of the claw 523 afor pressing the wafer 510 can be configured as that of a claw 523 bshown in FIG. 15B or configured as that of a claw 523 c shown in FIG.15C. That is to say, these claws 523 a (523 b, 523 c) project inwardlyof the peripheral portion of the wafer 510. Assuming that the wafer 510fixed on such a prior art workpiece holder is irradiated with anelectron beam while a retarding voltage is applied to the wafer 510, thefollowing simulation of an electric field distribution is made.

FIGS. 16, 17A and 17B, and 18A and 18B each show a electric fielddistribution diagram showing the result of simulation of an electricfield distribution on the surface of the wafer 510 in the case where thewafer 510 is fixed on the workpiece holder 521 and is irradiated with anelectron beam 503 while a retarding voltage is applied to the wafer 510.In the figures, a plurality of lines designate equipotential lines 524connecting points having equal voltages to each other.

FIG. 16 shows the case where a central portion of the wafer 510 isirradiated with the electron beam 503, in which the trajectory of theelectron beam 503 is designated by the vertical line at the center ofthe figure. The equipotential lines 524 on the surface of the wafer 510extend in parallel to the surface of the wafer 510 up to the vicinity ofa shield electrode 541. In such a region, there does not occur anychange such as disturbance, that is, there is no dimensional effect dueto the retarding potential applied to the electron beam 503. Theequipotential lines 524 are separated from the surface of the wafer 510in the vicinity of the shield electrode 541.

FIGS. 17A and 17B are each an electric field distribution diagramshowing the result of simulation of an electric field on the surface ofthe wafer 510 in the case where a projection of the workpiece holder 521is 1 mm higher than an end portion of the wafer 510; wherein FIG. 17Ashows the case where an irradiated position with the electron beam 503is 5 mm separated from the projection, and FIG. 17B shows the case wherean irradiated position with the electron beam 503 is 10 mm separatedfrom the projection.

From the comparison between the results shown in FIGS. 17A and 17B, itis apparent that a variation in electric field in FIG. 17A is largerthan that in FIG. 17B, that is, the variation in electric field becomeslarger as the projection becomes closer to the irradiated position withthe electron beam 503. To be more specific, in a range, apart 5 mm fromthe projection, of the wafer 510, there is a high possibility that theelectric field is varied to disturb the irradiated position with theelectron beam 503.

FIGS. 18A and 18B are each an electric field distribution diagramshowing the result of simulation of an electric field on the surface ofthe wafer 510 in the case where an end portion of the wafer 510 projectsfrom the workpiece holder 521 to form a space under the end portion ofthe wafer 510; wherein FIG. 18A shows the case where an irradiatedposition with the electron beam 503 is 5 mm separated from the endportion of the wafer 510; and FIG. 18B shows the case where anirradiated position with the electron beam 503 is 10 mm separated fromthe end portion of the wafer 510.

From the comparison between the results shown in FIGS. 18A and 18B, itis apparent that a variation in equipotential lines 524 in FIG. 18A islarger than that in FIG. 18B. That is to say, as the irradiated positionwith the electron beam 503 becomes closer to the end portion of thewafer 510, the variation in equipotential lines 524 becomes larger tomake higher the possibility of disturbance of the irradiated positionwith the electron beam 503. Accordingly, it must be avoided to provide alarge space under the end portion of the wafer 510.

The above electric field simulation shows that if a high projection isprovided outside an end portion of the wafer 510 or a space is providedunder an end portion of the wafer 510, the outer limit of a range inwhich an irradiated position with the electron beam 503 is not disturbedis located at least 10 mm inwardly from the end portion of the wafer510.

From the above electric field simulation, it is also apparent that inorder to prevent a variation in electric field at an end portion of thewafer 510 and hence to prevent adverse effect exerted on an irradiatedposition with the electron beam 503, it is effective to make the heightof a portion, around the end portion of the wafer 510, of the workpieceholder 521 equal to the surface height of the wafer 510.

Depending on errors caused at the machining and assembling steps, it isdifficult to make the height of the wafer 510 perfectly equal to that ofthe workpiece holder 521; however, as the results of experimentsperformed by the present inventors, it is apparent that if a differencebetween heights of an end portion of the wafer 510 and workpiece holder521 is ±200 μm, the adverse effect of such a difference in heightexerted on an irradiated position with the electron beam 503 is almostnegligible.

With respect to the gap 537 shown in FIGS. 12 and 13, which is formedbetween the wafer 510 and holding plate 521 b (521 c) resulting from themachining accuracy, the results of experiments performed by the presentinventors show that if the gap 537 is 0.5 mm or less, the adverse effectof the gap 537 exerted on an irradiated position with the electron beam503 is almost negligible.

In this way, the electron beam application apparatus including thefunction of controlling an irradiation energy of an electron beam with aretarding voltage may be configured to prevent a variation in electricfield by making the height of a workpiece nearly equal to that of aworkpiece holder, setting a dimensional tolerance with respect to adifference in height between the workpiece and workpiece holder, orproviding a range of the workpiece in which the heights are nearly equalto each other. This makes it possible to irradiate an end portion of theworkpiece with the electron beam without reducing the accuracy of anirradiated position with the electron beam.

As described above, the electron beam application apparatus according tothe present invention, which includes the function of controlling anirradiation energy of an electron beam with a retarding voltage,exhibits the effect of irradiating a workpiece with an electron beamwithout reducing the accuracy of an irradiated position with theelectron beam.

What is claimed is:
 1. A circuit pattern inspecting apparatuscomprising: an irradiation optical system for converging a primarycharged particle beam while deflecting said primary charged particlebeam so as to scan a circuit pattern of a workpiece with said primarycharged particle beam; a retarding/accelerating means for retarding saidprimary charged particle beam, and accelerating secondary chargedparticles produced from said workpiece by the irradiation of saidworkpiece with said primary charged particle beam and reflectionparticles reflected from said workpiece; a workpiece stage for holdingsaid workpiece; a sensor for measuring the surface height of anirradiated position of said workpiece with said primary charged particlebeam; a detector for detecting said secondary charged particles producedfrom said workpiece; an image forming means for forming an image of theirradiated region of said workpiece from a signal detected by saiddetector; an outer peripheral sample having outer peripheral standardmarks formed on at least two surfaces different in thickness in thedirection of the axis of said primary charged particle beam, said outerperipheral sample being provided at an outer peripheral portion of asubstrate mounting area of said workpiece stage; a central sample havingcentral standard marks formed on at least two surfaces different inthickness in the direction of the axis of said primary charged particlebeam, said central sample being provided at a central portion of thesubstrate mounting area of said workpiece stage; a storing means forstoring image signals obtained from said outer peripheral standard marksof said outer peripheral sample and said central standard marks of saidcentral sample; a computing means for computing a distortion amount ofsaid primary charged particle beam inherent to said outer peripheralportion from said outer peripheral and central standard mark imagesignals; an eliminating means for eliminating said distortion amountinherent to said outer peripheral portion from said outer peripheralstandard mark image signals; a storing means for preparing a deflectioncorrecting table corresponding to the height of said workpiece on thebasis of said outer peripheral standard mark image signals from whichsaid distortion amount has been eliminated, and storing said deflectioncorrecting table; a deflection correcting signal generating circuit forobtaining a deflection correcting signal from said deflection correctingtable in accordance with the surface height signal from which saiddistortion amount has been eliminated obtained by said sensor; and acontrol means for controlling irradiation of said outer peripheralsample having said outer peripheral standard marks at a desired timingto update said deflection correcting table.
 2. A circuit patterninspecting apparatus comprising: an irradiation optical system forconverging a primary charged particle beam while deflecting said primarycharged particle beam so as to a circuit pattern of a workpiece withsaid primary charged particle beam; a retarding/accelerating means forretarding said primary charged particle beam, and accelerating secondarycharged particles produced from said workpiece by the irradiation ofsaid workpiece with said primary charged particle beam and reflectionparticles reflected from said workpiece; a workpiece stage for holdingsaid workpiece and having central standard marks formed on at least twosurfaces different in thickness in the direction of the axis of saidprimary charged particle beam; a sensor for measuring the surface heightof an irradiated position of said workpiece with said primary chargedparticle beam; a detector for detecting said secondary charged particlesproduced from said workpiece; an image forming means for forming animage of the irradiated region of said workpiece from a signal detectedby said detector; an outer peripheral sample having outer peripheralstandard marks formed on at least two surfaces different in thickness inthe direction of the axis of said primary charged particle beam, saidouter peripheral potion of a substrate mounting area of said workpiecestage; a calculating/storing means for calculating a deflectioncorrecting table corresponding to the height of said workpiece on thebasis of image signals obtained from said outer peripheral standardmarks of said outer peripheral sample, and storing said deflectioncorrecting table; a deflection correcting signal generating circuit forreceiving a signal of the surface height of said workpiece obtained bysaid sensor and obtaining a deflection correcting signal from saiddeflection correcting table in accordance with said surface height; anda control means for controlling irradiation of said outer peripheralstandard marks of said outer peripheral sample at a desired timing, toupdate said deflection correcting table and for outputting thedeflection correcting signal for correcting deflection of the primarycharged particle beam.
 3. A circuit pattern inspecting method comprisingthe steps of: converging a primary charged particle beam emitted from acharged particle source by an irradiation optical system whiledeflecting said primary charged particle beam so as to scan a circuitpattern of a workpiece mounted on a workpiece stage with said primarycharged particle beam; retarding said primary charged particle beam, andaccelerating secondary charged particles produced from said workpiece bythe irradiation of said workpiece with said primary charged particlebeam and reflection particles reflected from said workpiece; detectingsaid secondary charged particles produced from said workpiece; formingan image from a signal detected at said defecting step; measuring thesurface height of an irradiated position of said workpiece with saidprimary charged particle beam; acquiring image signals by irradiating,with said primary charged particle beam, an outer peripheral samplehaving outer peripheral standard marks formed on at least two surfacesdifferent in thickness in the direction of the axis of said primarycharged particle beam, said outer peripheral sample being provided at anouter peripheral portion of said workpiece stage and central standardmarks of a central sample being provided at a central portion of saidworkpiece stage; storing said image signals obtained from said outerperipheral standard marks of said outer peripheral sample, and imagesignals obtained from a central sample having central standard markssubstantially similar to those of said outer peripheral sample, saidcentral sample being provided at a central portion of said workpiecestage; computing a distortion amount of said primary charged particlebeam inherent to said outer peripheral portion from said outerperipheral and central standard marks image signals stored at saidstoring step; eliminating said distortion amount inherent to said outerperipheral portion from said outer peripheral standard marks imagesignals; and calculating a deflection correcting table corresponding tothe height of said workpiece on the basis of said outer peripheralstandard mark image signals from which said distortion amount has beeneliminated, and storing said deflection correcting table; obtaining adeflection correcting signal from said deflection correcting table inaccordance with the surface height signal obtained at said measuringstep; and controlling irradiation of said outer peripheral standardmarks of said outer peripheral sample at a desired timing, to updatesaid deflection correcting table.
 4. A circuit pattern inspecting methodcomprising the steps of: converging a primary charged particle beamemitted from a charged particle source by an irradiation optical systemwhile deflecting said primary charged particle beam so as to scan acircuit pattern of a workpiece mounted on a workpiece stage with saidprimary charged particle beam; retarding said primary charged particlebeam, and accelerating secondary charged particles produced from saidworkpiece by the irradiation of said workpiece with said primary chargedparticle beam and reflection particles reflected from said workpiece;detecting said secondary charged particles produced from said workpiece;forming an image from a signal detected at said detecting step;measuring the surface height of an irradiated position of said workpiecewith said primary charged particle beam; acquiring image signals byirradiating, with said primary charged particle beam, an outerperipheral sample having outer peripheral standard marks formed on atleast two surfaces different in thickness in the direction of the axisof said primary charged particle beam, said outer peripheral marks beingprovided at an outer peripheral portion of said workpiece stage andcentral standard marks of a central sample being provided at a centralportion of said workpiece stage; calculating a deflection correctingtable correction corresponding to the height of said workpiece from saidimage signals obtained from said outer peripheral standard marks on saidworkpiece, and storing said deflection correcting table; receiving asignal of the surface height of said workpiece obtained at saidmeasuring step and obtaining a deflection correcting signal from saiddeflection correcting table; controlling irradiation of said outerperipheral standard marks of said outer peripheral sample at a desiredtiming, to update said deflection correcting table; and outputting thedeflection correcting signal for correcting deflection of the primarycharged particle beam.
 5. A charged particle beam application apparatuscomprising: an irradiation optical system for irradiating one region ofa workpiece with a primary charged particle beam by deflecting saidprimary charged particle beam so as to scan said region of saidworkpiece with said primary charged particle beam; a workpiece stage forholding said workpiece; a retarding/accelerating means for retardingsaid primary charged particle beam, and accelerating secondary chargedparticles produced from said workpiece by the irradiation of saidworkpiece with said primary charged particle beam and reflectionparticles reflected from said workpiece; a sensor for measuring thesurface height of an irradiated position of said workpiece with saidprimary charged particle beam; a detector for detecting said secondarycharged particles produced from said workpiece and said reflectionparticles; an image forming means for forming an image from a signaldetected by said detector; an outer peripheral sample having outerperipheral standard marks formed on at least two surfaces different inthickness in the direction of the axis of said primary charged particlebeam, said outer peripheral sample being provided at an outer peripheralportion of said workpiece stage; a central sample having centralstandard marks substantially similar to those of said outer peripheralsample, said central sample being provided at a central portion of saidworkpiece stage; a storing means for storing image signals obtained fromsaid central standard marks of said central sample, comparing said imagesignals with those obtained from said outer peripheral standard marks ofsaid outer peripheral sample to obtain a distortion amount of saidprimary charged particle beam inherent to said outer peripheral portion,and storing said distortion amount; a computing circuit for eliminatingsaid distortion amount inherent to said outer peripheral portion fromsaid outer peripheral standard mark image signals; a calculating/storingmeans for calculating a deflection correcting table correctioncorresponding to the height of said workpiece on the basis of said outerperipheral standard mark image signals from which said distortion amounthas been eliminated, and storing said deflection correcting table; adeflection correcting signal generating circuit for obtaining adeflection correcting signal from said deflection correcting tablecorrection in accordance with the surface height obtained by saidsensor; and a control means for controlling irradiation of said outerperipheral standard marks of said outer peripheral sample at a desiredtiming, to update said deflection correcting table.
 6. A chargedparticle beam application method comprising the steps of: irradiatingone region of a workpiece with a primary charged particle beam bydeflecting said primary charged particle beam so as to scan said regionof said workpiece with said primary charged particle beam; retardingsaid primary charged particle beam, and accelerating secondary chargedparticles produced from said workpiece and reflection particlesreflected from said workpiece; measuring the surface height of anirradiated position of said workpiece with said primary charged particlebeam; detecting said secondary charged particles produced from saidworkpiece; forming an image from a signal detected at said detectingstep; acquiring image signals from an outer peripheral sample havingouter peripheral standard marks formed on at least two surfacesdifferent in thickness in the direction of the axis of said primarycharged particle beam, said outer peripheral sample being provided at anouter peripheral portion of said workpiece stage; storing image signalsfrom a central sample having central standard marks substantiallysimilar to those of said outer peripheral-sample, said central samplebeing provided at a central portion of said workpiece stage; comparingsaid image signals obtained from said standard marks of said outerperipheral and central standard samples with each other to obtain adistortion amount of said primary charged particle beam inherent to saidouter peripheral portion, and storing said distortion amount;eliminating said distortion amount inherent to said outer peripheralportion from said outer peripheral standard mark image signals;calculating a deflection correcting table corresponding to the height ofsaid workpiece on the basis of said outer peripheral standard mark imagesignals from which said distortion amount has been eliminated, andstoring said deflection correcting table; receiving the surface heightsignal obtained at said measuring step, and obtaining a deflectioncorrecting signal from said deflection correcting table in accordancewith said surface height; and controlling irradiation of said outerperipheral standard marks of said outer peripheral sample at a desiredtiming, to update said deflection correcting table.